Recent studies in rhesus monkeys have demonstrated an association of early developmental stress and decreased plasma measures of serotonin with increased incidence of maladaptive behaviors including aggression, poor impulse control and increased levels of alcohol self-administration. Similar relationships between plasma serotonin and maladaptive behaviors have also been described in humans. The objective of these experiments is to examine the potential role of reduced brain serotonin levels in the development of impulsive behavioral patterns in juvenile rhesus monkeys. We compare juvenile monkeys reared in peer groups with mother reared monkeys who are either intact or have been depleted of brain serotonin following administration of neurotoxic doses of MDMA. Initial comparisons focus on interactions in structured play groups, and performance in a computerized battery of cognitive tasks. Cognitive testing examines memory, attention, and executive function, as well as tasks designed to assess social cognition. Subsequent studies will examine the interaction of decreased central serotonin with the effects of acute alcohol administration, the incidence of excessive alcohol self-administration in a free-choice ethanol self-administration paradigm and the potential role of brain vasopressinergic neural substrates in the behavioral differences associated with rearing and serotonin.